Hitherto, a series of benzopyran derivatives has been known to have various pharmacological activities. For example, Japanese Patent Application (Kokai) Nos. Sho-60-97974, Sho-61-47416, Sho-63-165317, Sho-63-196581, Sho-63-201182, Sho-63-303977, Sho-64-26578, Sho-64-38087 and Hei-2-129184, and Journal of Medicinal Chemistry, Vol. 33, No. 6, pages 1529-1541, 1990, etc. disclose various benzopyran derivatives in which the carbon atom at the 4-position of the benzopyran ring is directly bonded to a nitrogen atom, and these compounds have been described as having an antihypertensive activity and being usable for the treatment of cardiac disorders, etc.
Further, Japanese Patent Application (Kokai) Nos. Sho-63-303977 and Sho-64-38087, WO 90/14346 and WO 92/14439, Journal of Heterocyclic Chemistry, Vol. 11, No. 5, pages 797-802, 1974, etc. disclose benzopyran derivatives in which the carbon atom at the 4-position of the benzopyran ring is not directly bonded to a nitrogen atom.
WO 90/14346 and WO 92/14439 disclose compounds having a general formula which includes, within its scope, a part of the compounds of the present invention wherein the 4-position of the benzopyran ring is substituted with an amido group or a thioamido group. Further, WO 92/14439 discloses compounds of the general formula which includes, within its scope, the compounds of the present invention and describes that these compounds are useful as a trichogenous agent. More specifically, WO 92/14439 discloses the compounds which include the compounds of the present invention and which are represented by the general formula: ##STR2## wherein X represents .dbd.O, .dbd.S, .dbd.N--Z or .dbd.CHNO.sub.2, in which Z represents a hydrogen atom, a lower alkyl group, an aryl group, a hydroxy group, a lower alkoxy group, a cyano group, a carbamoyl group or a sulfamoyl group; Y represents --NR.sub.8 R.sub.9, --OR.sub.10 or --SR.sub.11, in which R.sub.8 and R.sub.9 may be the same or different and each represents a hydrogen atom, a hydroxy group, a lower alkoxy group, a cyano group, an amino group which may have (a) substituents, a lower alkyl group which may have (a) substituents, an unsaturated lower alkyl group which may have (a) substituents, a cycloalkyl group which may have (a) substituents, an aryl group which may have (a) substituents, a heteroaryl group which may have (a) substituents, or, when taken together with the nitrogen atom, R.sub.8 and R.sub.9 jointly represent a heterocyclic group which may have (a) substituents, R.sub.10 and R.sub.11 each represents a hydrogen atom, a lower alkyl group or an aryl group; R.sub.1 represents a hydrogen atom, a lower alkyl group or an aryl group, or forms a single bond when bonded directly to R.sub.2, R.sub.2 and R.sub.3 may be the same or different and each represents a hydrogen atom or a hydroxy group, or, when taken together, form .dbd.O; R.sub.4 and R.sub.5 may be the same or different and each represents a hydrogen atom or a lower alkyl group which may have (a) substituents, or, when taken together, represent a polymethylene group; R.sub.6 and R.sub.7 may be the same or different and each represents a hydrogen atom, a lower alkyl group, a lower haloalkyl group, a halogen atom, a lower alkoxy group, a lower haloalkoxy group an amino group, an acylamino group, a nitro group, a cyano group, an ester group, a lower alkylsulfonyl group or an arylsulfonyl group, or, when taken together, represent .dbd.N--O--N.dbd.. However, this publication does not specifically describe the structure and the name of the compounds of the present invention and further does not suggest at all that the compounds of the present invention exhibit an unexpectedly remarkable effect as a potassium channel opener.
In these conventional compounds, cromakalim is now developed as a new type of hypotensive agents, but the activity thereof is still unsatisfactory. Also, some other compounds have an activity higher than that of cromakalim, but many of them have problems from the aspect of safety since they exhibit disturbance of organs such as the lungs and have a property of mutagenicity.
As a result of extensive studies by the present inventors with respect of compounds having a potassium channel activity higher than that of the conventional closely-related compounds including a typical cromakalim and having fewer problems from the aspect of safety, the present inventors found that the compounds of the present invention solve the conventional problems and exhibit an excellent effect as a pharmaceutical agent and completed the present invention.